Navigation services use positional data to locate vehicles or devices. A simple location on its own may not be useful to a user. For example, the location is matched to a digital map. Map matching is the process used to match the location to a digital map. Algorithms and software are used to associate or match the location with a known position on a map, e.g. a correct road segment.
For location data such as from the global positioning system, there exists the possibility for errors or inaccurate measurements. An accurate location determination from a global positioning service (GPS) receiver requires line of sight with GPS satellites. Satellite geometry also becomes an issue when using a GPS receiver in a vehicle, near tall buildings, or in mountainous or canyon areas. When the GPS signals are blocked from several satellites, the relative position of the remaining satellites determines how accurate the GPS position will be. As more and more of the sky is obstructed by buildings or terrain, it becomes increasingly difficult to accurately determine a position.
Another source of error is multipath. Multipath is the result of a radio signal being reflected off an object. With GPS, multipath occurs when the signal bounces off a building or terrain before reaching the GPS receiver's antenna. The signal takes longer to reach the receiver than if the signal traveled a direct path. The added time makes the GPS receiver calculate that the satellite is farther away than the satellite really is. The added time increases the potential for error in the overall position determination. Propagation delay due to atmospheric effects and internal clock errors may also affect accuracy.
Errors or inaccurate measurements for positional data may lead to incorrect map matches. Incorrect map matches may result in severe consequences for both the mapping service and an end user. One technique to limit errors is to use complex algorithms that use multiple inputs (other than just position) for map matching.